Title: S-nitrosothiol-regulated pathways in acute lung injury Abstract (245 words) Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is characterized by an initial airway inflammatory insult that results in diffuse alveolar damage and the subsequent development of respiratory failure. Despite an incidence of ~200,000 cases/year in the United States and mortality rate approaching 40%, no effective therapy exists to treat ALI/ARDS. S-nitrosothiols (SNOs) are endogenously-produced, bioactive forms of nitric oxide that function to inhibit immune response pathways in the respiratory epithelium. Recently, we demonstrated that airway SNOs are acutely depleted in a mouse model of ALI and that treatment with inhaled ethyl nitrite (ENO), an S-nitrosylating agent, protects from the development of lung injury. However, the molecular targets of SNOs in the lung airway remain to be discerned. We hypothesize that proteomic signatures derived from analysis of airway lining fluid can be used to elucidate the SNO-regulated immune response pathways in ALI which underlie the pharmacological basis of ENO therapy. Accordingly, we propose to: 1. Characterize the effects of ENO treatment on the airway proteome in ALI and identify signaling pathways that are affected by SNO repletion; and 2. Identify BALF proteins that are modified by S- nitrosylation in ALI and determine the effects of S-nitrosylation on their inflammatory activities.. Completion of these specific aims should provide a fuller understanding of SNO-regulated pathways in the airways and will guide the further study of SNO-based therapy for the prevention and resolution of inflammatory lung injury.